1. Field of the Invention
The present invention relates to a washing machine, and more particularly, to a laundry amount sensing apparatus and method for a washing machine which can precisely detect a laundry amount by using a correlation between an inclination of a wash tub and a laundry amount.
2. Description of the Background Art
In general, a washing machine applies a mechanical operation such as friction or vibration to the laundry put into a washing solution, thereby separating contaminants from the laundry.
The washing machine performs a washing step that applies a mechanical force to the laundry mixed with the washing solution, a rinsing step that separates the washing solution containing contaminants from the laundry, and a spin-drying step that removes rinse water from the laundry.
When the laundry is not evenly distributed in the washing machine, namely, when the laundry is unbalanced, serious vibration and noise occur in the spin-drying operation.
Therefore, the washing machine needs a laundry leveling function that detects unbalanced laundry and evenly distributes the laundry according to the detected unbalance.
FIG. 1 is a schematic diagram illustrating a structure of a conventional drum type washing machine.
Referring to FIG. 1, the conventional drum type washing machine includes: a housing 11 that provides the shape of a main body; a suspension device 12 including a spring and a damper in the housing 11; an outer water tub 13 supported by the suspension device 12; a drum type inner rotating tub 14 positioned in the outer water tub 13, for washing the laundry; a driving unit 15 for rotating the inner rotating tub 14; and a rotation shaft 16 for transferring a driving force of the driving unit 15.
In the washing and rinsing operations of the drum type washing machine, water is supplied to the inner rotating tub 14. When the water level in the inner rotating tub 14 reaches an appropriate water level, the supply of water is stopped.
The inner rotating tub 14 is repeatedly rotated in the forward or backward direction by the driving force generated by the driving unit 15.
In the spin-drying operation, water supplied to the inner rotating tub 14 is drained off. The inner rotating tub 14 is first rotated at a low speed in the forward or backward direction by the driving force of the driving unit 15 for performing the laundry leveling function and then is accelerated to a spin-drying speed for performing the spin-drying operation.
The spin-drying operation needs precise sensing of the amount of laundry in the inner rotating tub 14.
As shown in FIG. 2, a conventional laundry amount sensing method for a drum type washing machine calculates a sum of PWM duties required to reach a specific RPM, and a sum of RPM errors generated in a specific period maintaining the specific RPM.
The difference between the sum of the PWM duties required to reach the RPM and the sum of the RPM errors is determined as a laundry amount data.
However, the conventional laundry amount sensing method for the drum type washing machine drives the motor of the washing machine to sense the laundry amount, which increases power consumption.
In addition, the conventional laundry amount sensing method for the drum type washing machine cannot precisely sense the laundry amount according to the laundry quality.
Furthermore, the conventional laundry amount sensing method for the drum type washing machine does not sense the laundry amount by a single load, thereby causing an unbalance sensing error.